The present invention relates to a device for use in drying materials, especially particulate, granular or powdered materials, but also materials in liquid form, in a drying chamber in which the material is set in motion. An embodiment of the invention has been developed especially for handling of fish-related products such as crushed fish offal as well as chemical residues and waste products, but the inventive concept may be applied to practically all types of material with similar consistency and drying requirements.
In drying of materials of the above-mentioned types, extensive use is made of rotating, horizontally located drums which are heated, or the material is placed in a drying chamber, where it is whirled round in a warm environment in order to effect drying. These drying devices may provide satisfactory drying, but the degree of dryness achieved for the material being treated can often be uneven, and it can be difficult to achieve the exact drying effect desired without the use of sophisticated aids.
In patent publication EP-A2-0 696 715, moreover, the use is disclosed of a circular cylindrical drying chamber with vertical straight walls and a movement device in the bottom. The material moves up in the chamber as it dries and can be removed from the top portion of the chamber.
DE 3819945 describes a drying device for drying particulate, granular or powdered material, comprising a drying chamber (1) with means for moving the material and means for heating the material, whereby the drying chamber (1) is conically tapering over its entire, or parts of its height. The device further has a movement device and a heating jacket. The material to be dried is however constantly supplied with a gas (preferably heated) through the outlet (9) in the rotational axle (7), which also rotates the movement device (8). The added air is then ventilated off at the top.
DE 2239098 further describes a drying chamber where the substance to be dried is constantly ventilated with ambient air or other gas.
This is also the case with the drying apparatus in GB 2019994 where the products to be dried moves in a downward direction and added gas moves in the upward direction, and the gas and the substance to be dried is constantly mixed in the drying chamber, The chamber is also fitted with an external heating jacket.
On the basis of previously known solutions as mentioned above, according to the present invention a device has been provided where the drying chamber is conically taperingly formed towards the drying chamber""s upper or lower portion, thus enabling a further favourable movement to be achieved in the partially dried and gradually almost completely dried material in comparison with a drying chamber with straight vertical walls.
If the drying chamber is conically tapering towards the drying chamber""s upper portion the incompletely dried material which rises in the chamber will be able to be moved towards the chamber""s centrally located area and fall down there. This in turn will lead to an accumulation of incompletely dried material in the centrally located area in the chamber""s lower part and this material undergoes a new movement along the drying chamber""s walls. In a design of this kind only the material which attains the desired degree of dryness will be permitted to be discharged and this can be controlled according to requirements. The design is suitable, amongst other things, for drying individual batches of material (batch drying).
If the drying chamber is conically tapering towards the drying chamber""s lower portion, the gradually dried material will be able to move along the walls in the drying chamber towards the drying chamber""s upper portion. This is further facilitated by the fact that the drying chamber is conically taperingly formed towards the drying chamber""s lower portion. The material which has not yet attained the desired degree of dryness is prevented from moving towards the centrally located area of the chamber to fall down there and lie in the area at the bottom of the drying device. This design is therefore well suited for a continuous process where the material is constantly ejected when it attains the desired degree of dryness. In addition it is possible with this design to achieve a uniform or almost uniform thickness of the layer of material which abuts against the drying chamber""s walls.
The object of the present invention is to provide a device which offers a simple drying process, while at the same time the efficiency of the drying is easily controllable, and where an identical degree of dryness is ensured for the entire quantity of material.
According to the invention the device is further designed in such a manner that it can be adapted to suit the material which is inserted, the drying chamber being conically tapering over its entire height or parts of its height towards the top or the bottom of the drying chamber.
According to the invention a device is provided where in a preferred embodiment a vertically standing, preferably circular cylindrical container is employed as drying chamber. The drying chamber preferably has a conically tapering form either towards the drying chamber""s upper or lower portion depending on which material has to be dried and whether this has to be undertaken in a continuous process or a batch process. The degree of tapering may be relatively small, between 0.1 and 10 degrees and generally round 0.5 degrees relative to the vertical plane in the chamber.
The device is provided with heating of the conical walls, at least over a substantial part of the wall surface, together with a movement device which flings the material against these heated walls. As the material is heated and dried, the material will become lighter, thereby being forced upwards in the vertical container towards an outlet in the top area. When setting the force from the movement device the dwell time in the cylinder can be set and coordinated with heating of the walls, with the result that when it reaches the outlet the material has the desired degree of dryness. The material can be fed continuously into the drying chamber in the bottom area by the movement device, which may, e.g., be a screw, and as it is dried may be permitted to continuously flow out in the top area. It will also be possible to feed in a specific quantity of material which is then set in rotary motion and when the material has reached the desired degree of dryness the chamber is emptied. It may further be advantageous for some types of material to perform this drying process without the presence of air in the drying chamber and for this purpose the chamber may be equipped with an end piece in order to provide an underpressure in the interior of the drying chamber.
The material may be inserted through a slanting inlet where the force of gravity forces the material into the drying container or it may be fed in by a driven feeding device. The insertion is performed in an embodiment in the lower portion of the walls in the drying device. In an embodiment the inlet to the device""s drying chamber will be provided with a valve body which controls the introduction of material which has to be dried. Moreover, in a further embodiment a feed is provided in the drying device""s upper part and this may be installed in the lid of the device. The feed in both the upper and lower portions may be used with a conical shape tapering both towards the upper and lower portions.
The invention can be used for drying of practically any material which can be caused to circulate in a container. However, the invention is especially intended for materials such as fish-related products, for example crushed fish offal, chemical residues and waste products, preferably in particulate form, but also in almost liquid form. After drying such products can be transported at a more reasonable price, since they are lighter in weight and easier to handle.